import Stream from 'stream'
const Readable = Stream.Readable //可读流，用于接收数据
const Writable = Stream.Writable //可写流，用于发送数据
const Duplex = Stream.Duplex  //可读可写流|双工流，既可读又可写
const Transform = Stream.Transform //变换流，既可读又可写，并能对数据进行修改。